When lifting a wind turbine nacelle in order to place it on top of a wind turbine tower, a crane with a yoke and wires is normally used. The nacelle is transported to the site of the tower, after which the yoke is attached to the nacelle at four points, substantially one point at each corner of the nacelle, via wires, and the nacelle is lifted by the crane.
The yoke comprises a complex arrangement of hydraulics to be able to adjust the position of the nacelle during the lift, such that the nacelle is in the correct, horizontal, position when placed on the tower. The hydraulics of the yoke is also needed to attach the yoke to the four corners of the nacelle since the nacelle is often transported in a non-horizontal, inclining, position to save space. The yoke thus needs to be hydraulically tilted to reach the lower end of the inclined nacelle, after which the yoke is tilted back to give the nacelle a horizontal attitude.
The yoke described above is rather large and complex, and thus expensive.